1. Field of the Invention
The present invention relates to a valve structure for a control valve suitably applied to a fluid pressure control valve which variably controls the outgoing fluid pressure and to a fluid flow control valve which variably controls a rate of the output fluid flow therethrough, and specifically to an electromagnetic solenoid-type fluid pressure control valve which is applied to a hydraulic brake system with an anti-skid brake control system generally abbreviated as an "ABS" and/or a traction control system generally abbreviated as a "TCS", and further to an electromagnetic solenoid type fluid flow control valve which is applied to a steering effort control system for an automotive vehicle in which the steering effort can be suitably controlled depending on the vehicle speed.
2. Description of the Prior Art
Recently, there have been proposed and developed various electromagnetic solenoid type fluid pressure control valves which can properly vary the incoming fluid pressure to generate a controlled fluid pressure to a fluid-pressure operated actuator, such as a vehicle wheel cylinder. For example, Japanese Utility Model First Publication (Jikkai Heisei) No. 3-68685 discloses an electromagnetic solenoid type fluid pressure control valve which includes a valve housing with an axial bore and a substantially cylindrical valve spool slidably enclosed in the axial bore. Such a pressure control valve is usually arranged between an external fluid pressure source and a fluid-pressure operated actuator such as a wheel brake cylinder, so as to suitably control the outgoing fluid pressure therethrough to the actuator. The valve spool itself is integrally formed with a pair of solenoid plunger portions at both ends of the central valve portion of the valve spool. The respective solenoid plungers are arranged axially to the central valve portion in such a manner as to extend in the opposing axial directions of the valve spool. Therefore, the axial length of the valve spool would become large.
Japanese Patent First Publication (Tokkai Shows) No. 3-65461 discloses a brake control system for automotive vehicles, which is applied commonly to an anti-skid brake control and a traction control. The brake control system includes a master-cylinder equipped with a hydraulic brake force booster, four three-port/three-position, electromagnetic solenoid-type switching valves which are included in the ABS and arranged parallel to each other between the master cylinder and the respective wheel cylinders, and two two-port/two-position electromagnetic solenoid-type switching valves which are included in the TCS and arranged in the brake fluid line between the master cylinder and the driven-wheel cylinders. As appreciated from the above, the brake control system disclosed in the Japanese document No. 3-65461 requires a number of electromagnetic solenoid-type switching valves for an anti-skid brake control executed during deceleration slip and a traction control executed during acceleration slip. The above-mentioned plural switching valves are not integrally formed as a single unit, but constructed independently of each other. Thus, the prior art system suffers from the drawback that the entire size and whole weight of the system tend to be both enlarged to provide many advantageous functions, namely a deceleration-slip control, an acceleration-slip control, the functioning of a hydraulic brake booster, or the like. It is troublesome to install the brake control system in a relatively narrow limited space of the vehicle.